1. Technical Field
The present invention relates to an apparatus for automatically recovering a speech path of a telephone terminal in a telephone system, and more particularly, relates to an apparatus for automatically recovering a speech path of a telephone terminal whenever a handset is inadvertently left off-hook.
2. Related Art
Generally, telephone systems having a handset must be placed in an on-hook status in order to receive an incoming call. Voice network used during telephone conversation must be disconnected from the telephone lines so that a ring detection unit can respond to the incoming call and generate a ring signal to alert the user of such an incoming call. However, there are instances where the telephone can be inadvertently left off-hook which results in an out-of-order status and consequent loss of incoming call service at least until the user discovers the problem and hangs up the telephone. Such instances typically occur when the user carelessly misplaces the handset and improperly hangs up the telephone. When the handset is carelessly misplaced, an off-hook alert signal in a form of a "howler" tone or a set of distinct audio tones is transmitted from an exchange system to a telephone left off-hook for a period of time in order to alert the user of such an out-of-order status and to remind the user to hang up the telephone. The off-hook alert signal is usually terminated after a short period of time, however. If the user is not in the proximity of the telephone to hear the off-hook alert signal, then the telephone can remain out-of-order for a long period of time.
Consequently, means for automatically restoring service to a telephone that is inadvertently left off-hook has been developed to improve the serviceability and dependability of such telephones. Contemporary apparatus for restoring an off-hook telephone back to an on-hook condition in order to receive incoming calls are disclosed, for example, in U.S. Pat. No. 3,150,237 for Telephone Line Clearing Relay issued to Baldik et al., U.S. Pat. No. 4,109,112 for Telephone Isolation Device issued to Denman et al., U.S. Pat. No. 4,922,529 for Automatic Hangup Apparatus For Restoring Service To Off-Hook Telephones issued to Kiel, U.S. Pat. No. 4,998,271 for Telephone Accessory issued to Tortola et al., U.S. Pat. No. 5,592,529 for Telephone Inadvertent Off-Hook Condition Detector issued to Linsker, U.S. Pat. No. 5,606,593 for Apparatus And Method For Automatically Returning A Telephone Set To An On-Hook Condition issued to Smith, and U.S. Pat. No. 5,612,997 for Off-Hook Disconnect And Reconnect Ringer Device issued to Wallelonga, Sr. et al., and Korea Utility Model Publication No. 94-2280.
For example, U.S. Pat. No. 3,150,237 issued to Baldik et al., discloses a relay switch mechanism which is mechanically coupled to a cradle switch for disconnecting an off-hook telephone from the telephone line in order to restore service to the user. U.S. Pat. No. 4,109,112 issued to Denman et al., discloses a telephone isolation device which uses a magnetic latching relay having restore and disconnect coils for disconnecting the inadvertently left off-hook telephone from the telephone lines. U.S. Pat. No. 4,922,529 issued to Kiel discloses an automatic hang-up apparatus for restoring services to off-hook telephones. The Kiel apparatus monitors for occurrences of: (1) a characteristic howler sent by a local exchange system to warn the telephone customer that the telephone is off-hook, (2) a long period of silence where there is no dial tone, or (3) no movement of a handset for a period of time. Occurrence of any of these is considered an inadvertent off-hook status and the apparatus is automatically switched to an on-hook status. The Kiel apparatus requires, however, a litany of sensor circuits such as an off-hook sensor using relay coils, howler tone sensor, silence sensor including a timer, dial toner sensor, and motion sensor, which all add complexity to a telephone. U.S. Pat. No. 4,998,271 issued to Torlola et al., and U.S. Pat. No. 5,592,529 issued to Linsker also describe detection of a howler tone sent from the local exchange system and other audio signals in order to alert the user that the telephone is in an off-hook condition. U.S. Pat. No. 4,686,700 for Telephone Off-Hook Detector Circuit issued to Perry, U.S. Pat. No. 4,731,829 for Circuit For Detecting Current Variations issued to Bonnet et al., and U.S. Pat. No. 5,140,631 for Apparatus and Method For Determining The State Of A Telephone Line issued to Stahl, describe only detection of the on-hook or off-hook condition of a telephone for subsequent operations.
U.S. Pat. No. 5,390,249 issued to Park and Korean Utility Model Publication No. 94-2280 disclose a speech recovery circuit using three relays connected in parallel to the telephone lines for receiving incoming calls when the telephone handset is placed in an abnormal manner. Similarly, both recent U.S. Pat. No. 5,606,593 issued to Smith and U.S. Pat. No. 5,612,997 issued to Vallelonga, Sr. et al., disclose an apparatus which includes at least one relay switch for detecting if a telephone is off-hook and automatically returning an off-hook telephone back to an on-hook condition in order to receive an incoming call.
As I have noted however, conventional speech path recovery apparatus necessarily requires the use of relay switches and other communication operation and maintenance circuits. Consequently, the quality of voice communication can deteriorate due to coils of the relay, and the production cost of such an apparatus can be increased.